Ink jet printers are a popular form of printer used with computers and similar applications involving document printing or graphics preparation. Typical ink jet printers, such as those manufactured by Original Equipment Manufacturers (OEMs) such as Hewlett Packard, have replaceable ink jet cartridges with built-in printheads. While such OEM ink jet cartridges are a convenient manner of supplying ink to such printers, the cartridges are necessarily expensive due to their complexity and the provision of printheads with the cartridges.
Cartridges provided by printer manufacturers are typically not designed to be refilled when the ink supply runs out. It is well known, however, that such cartridges and their associated print heads have useful lives significantly longer than that provided by the initial supply of ink. Therefore, an aftermarket industry has evolved, that is directed to providing systems for refilling cartridges with ink. The need to provide ink refilling is especially acute in the case of color ink cartridges, because typically one color will run out of ink before the other colors are depleted.
Refilling ink cartridges with ink is not an easy task. First, some means must be provided to supply the ink to the interior of the cartridges. Because the ink reservoirs are typically filled with foam sponge, the ink refilling process is slow due to slow absorption of ink by the foam. Users typically do not have the patience to refill slowly (typically by squeezing a refill reservoir or by gravity feed), and this causes ink to flow into the foam sponge at a rate that is usually too fast to be absorbed. Ink accumulates in the bottom of the cartridge and overflows from the top and from the printhead.
To help speed the process, some refilling mechanisms of the prior art pressurize the ink while refilling the cartridge. See, e.g., U.S. Pat. No. 6,945,640 to Cheok, incorporated by reference herein. Such pressurization merely exacerbates an air injection problem, by inducting air along with the ink filling the cartridge, and by preventing the removal of air from the foam sponge. The air injected into the foam sponge reservoir during refilling causes vapor lock in the ink reservoir. Ink then cannot reach the printhead, and the printer fails. In order to overcome this problem, Cheok teaches that the air must subsequently be removed through vacuum evacuation of the cartridge. However, Cheok does not teach how much ink to add to the cartridge.
Prior art refilling mechanisms may not inject the proper quantity of ink into the reservoir. Such overfilling may bind the internal cartridge ink pump, create a mess from weeping ink, and may prevent the cartridge from functioning properly.
In order to avoid vapor lock, U.S. Pat. No. 4,967,207 to Ruder teaches completely evacuating the cartridge, and then supplying ink to refill the cartridge. In essence, Ruder improperly teaches that the vacuum within the cartridge will suck the proper amount of ink back into it. However, it is impossible to achieve a perfect vacuum. If the cartridge could structurally withstand a near perfect vacuum without being damaged, in Ruder's process, the cartridge would be completely filled with ink, and thus would be overfilled. A less than perfect vacuum will not fill the cartridge completely. A properly filled cartridge has a precise quantity of ink, and a certain amount of airspace. Therefore, Ruder does not solve the ink quantity problem.
U.S. Pat. No. 4,968,998 to Allen discloses refilling the cartridge while evacuating, such that the evacuation rate exceeds the filling rate. This Patent states that the cartridge can never be overfilled; however, if the air is completely removed from the cartridge, which would eventually happen by Allen's method, the airspace in the cartridge would no longer exist.
U.S. Pat. No. 5,903,292 to Scheffelin et al. teaches refilling a spring-loaded collapsible ink bag, which maintains a negative pressure to draw ink into the bag until it is substantially full. However, many commercially available print cartridges are not constructed with such spring loaded bags.
Another prior art solution to these refilling problems is a “Clip-In” type refill system. The original ink cartridge is modified by removing all of the original ink reservoirs, such that only the printheads and the case are left. Removable ink reservoirs are supplied, so the user only has to change the ink reservoir assembly causing no mess. The disadvantage of this system is that it the user must be supplied with a pre-modified cartridge specially-adapted for use only with the removable ink reservoirs, and in practice, this system is nearly as costly as OEM printer cartridges.
Thus, there presently exists a need for a simple method and apparatus for refilling printer ink cartridges that eliminates the problems of slow refilling, overfilling and potential vapor lock.